Bacterial contamination of drilling fluids contributes to a number of problems in the oil field. First, many of the muds contain sugar based polymers in their formulation that provide an effective food source to bacterial populations. This can lead to direct degradation of the mud. In addition, bacterial metabolism can generate deleterious products, most notably hydrogen sulfide that besides being a toxic gas can lead to decomposition of mud polymers, formation of problematic solids, such as iron sulfide, and/or corrosive action on drilling tubes and drilling hardware.
Efforts to control bacterial activity in drilling fluids has been moderately successful. One of the more effective biocides to date is XCIDE 102 (XC 102) sold by Baker Petrolite, a glutaraldehyde-based biocide. However, XC 102 can be problematic because it is hazardous to handle and has environmental concerns.
U.S. Pat. No. 4,552,591 describes a biocide that is a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a weight ratio of the former to the latter being about 94% to about 64%, adsorbed on a solid, particulate adsorbent. This biocide is sold as XCIDE 207 (XC 207) by Baker Petrolite.
One product that shows potential under these constraints is MAGNACIDE 575. MAGNACIDE 575 or tetra-kis-hydroxymethyl-phosphonium sulfate (THPS) is a quaternary phosphonium salt that can effectively control bacterial growth in a number of systems. MAGNACIDE 575 is available from Aquaness Chemicals (Baker Petrolite) in 75% active liquid form, as well as in a 35% active form. Liquids are difficult to apply in stimulation and drilling applications. Some customers are reluctant to use an expensive liquid such as MAGNACIDE 575 because of potential financial losses due to spills such as may occur during handling and shipping. For instance, it is difficult for a field fracturing operator to climb atop a 20,000 gallon frac tank carrying gallon jugs of liquid biocide. MAGNACIDE 575 has the significant advantage of being "environmentally friendly".
It would thus be desirable to develop a composition and method employing it which did not involve the use of a liquid biocide.